The invention relates to improvements in apparatus for testing the brake systems of motor vehicles, and more particularly to improvements in testing apparatus of the type wherein a mobile depressing unit can engage and depress the pedal of the brake system in a motor vehicle.
It is already known to employ a portable brake testing apparatus which can be installed in a motor vehicle and has means for depressing the brake pedal. An apparatus employing such depressing means can be equipped with an integrated distance sensing device to monitor the distance which is covered by the depressing means, and with an integrated force sensing device to generate signals denoting the magnitude of force which is required to depress the pedal in order to achieve a certain braking action. Reference may be had to German Pat. No. 29 28 153 which proposes to affix a stationary part of the testing apparatus to the steering column and to employ a pneumatic motor which can move a plunger or a like part against the brake pedal. The plunger includes three rods the front end portions of which are connected to each other by a crosshead. The distance sensing means of the patented apparatus is a rotary encoder or a pulse generator and is actuated by one of the rods which form part of the pneumatically movable plunger. The force sensing means of the patented apparatus includes a load cell which is installed in the crosshead. A drawback of the patented apparatus is that its measurements are not sufficiently reliable, especially as concerns the indications which are furnished by the force sensing means.
Similar brake testing apparatus are disclosed in U.S. Pat. Nos. 4,186,595 and 4,307,604. A somewhat different brake testing apparatus is disclosed in U.S. Pat. No. 3,662,593.